An omnimagnetic field generator, or Omnimagnet, is a novel electromagnet that can potentially be used to remotely detumble electrically conductive, nonmagnetic space debris objects via eddy currents. Omnimagnets use three concentric, orthogonal copper solenoids wound around aluminum frames to generate magnetic fields. Operating an Omnimagnet generates large amounts of Joule heating in the solenoids, which can lead to overheating and device failure. Radiative cooling at the outermost surfaces is the only mechanism for heat dissipation. Heat dissipation of the innermost components is limited by the concentric geometry, causing elevated temperatures. Omnimagnet systems cannot be designed without understanding the relationships between Joule heating, Omnimagnet size, and detumbling capability, which are not adequately captured by existing models. The goal of this work is to calculate the detumbling capability of Omnimagnets in space while ensuring overheating does not occur. This work develops a finite element analysis (FEA) model to simulate Omnimagnet thermal behavior in space. Model results show that the innermost Omnimagnet components reach higher temperatures than the outermost components due to limited heat transfer pathways. Applying a high- emissivity coating to aluminum surfaces leads to increased radiative cooling, allowing for a 14% increase in applied current density without overheating. Scaling relationships between nondimensional Omnimagnet length and radiative cooling, maximum current density and magnetic dipole moment are developed to predict the detumbling capability of any size Omnimagnet. These scaling relationships show that radiative cooling scales approximately with nondimensional length squared. This relationship allows the prediction of the upper limit of heat generation via Joule heating. The applied current density scales with nondimensional length to the-0.686 power. Larger Omnimagnets must reduce current density because radiative cooling and Joule heating scale differently with nondimensional length. Magnetic dipole moment scales with nondimensional length to the 3.538 power, indicating that large Omnimagnets produce substantially stronger magnetic fields. Larger Omnimagnets are more efficient per mass than smaller Omnimagnets, which is critical for space applications. This work establishes the critical dependence of Omnimagnet size and detumbling capability on thermal behavior, marking the first step in thermally guided Omnimagnet design. Additionally, it identifies the significant role that surface radiative properties, such as emissivity, can play in enhancing thermal performance, further advancing the potential for successful detumbling missions in space.

Omnidirectional magnetic field generators, or Omnimagnets, are electromagnetic devices used for non-contact manipulation tasks. Supplying current to an Omnimagnet generates a magnetic field and generates Joule heating, which can cause overheating. Omnimagnets are thermally limited. Omnimagnet design currently relies on advanced thermal-electromagnetic simulations, which can vary widely between applications. Currently, there is no generalized understanding for coupled thermal-electromagnetic effects. This work addresses this knowledge gap by developing a universal framework for estimating Omnimagnet performance directly from the design and operating conditions. Scaling analysis is used to determine the coupling between thermal and electromagnetic effects in terms of design variables and base principles. The scaling relationships are used to define a figure of merit η where a higher η indicates a superior design. Equations are fitted to simulated Omnimagnet performance for multiple cooling mechanisms (convection, radiation) and different electromagnetic priorities (dipole moment m, m/mass). Quantitative relationships are developed that can predict Omnimagnet performance across a spectrum of designs without requiring advanced thermal and electromagnetic simulations (i.e. [Formula: see text] 530[Formula: see text] for convectively-cooled Omnimagnets, where [Formula: see text] is the figure of merit). The figure of merit η can also be used to gauge Omnimagnet performance for new applications, as is shown for power-sensitive Omnimagnets. Using this methodology, non-experts can use a figure of merit to streamline the design of Omnimagnets for new or existing use cases. The methodology is broadly applicable for the design of similar electromagnetic devices such as electrical motors, generators, and electromagnets.

Metal additive manufacturing (AM) is an increasingly important technology for producing complex metal parts. Residual stress can cause unwanted distortion of printed parts, particularly for thin (high aspect ratio) features. Highly transient and localized thermal phenomena, which are not well understood due to a lack of experimental data, may lead to excessive residual stress buildup in the part. To investigate residual stresses, this work designs and implements a novel in situ measurement method to measure the 2-D temperature history at the bottom of a 500 μm-thick Inconel plate, which acts as a thermal analog for a real printed part. The top surface of the Inconel 625 plate was subject to laser heating while a high-speed infrared camera measured the thermal radiance at the bottom of the plate, representing the thermal behavior inside a part at a depth of 500 μm. A one-dimensional thermal analysis was utilized to confirm that the 500 μm-thick plate would demonstrate a similar thermal response relative to a bulk, thick part and especially overhang geometries undergoing LPBF. This measurement method allows for the first temperature visualization in the x-y (scan and hatch) plane below the top surface. The temperatures at the bottom surface were studied for laser power P= 250–300 W, scan speeds v= 200-400 mm/s, and multiple scan strategies. Temperatures above 750 °C were observed at the bottom surface, and melting was observed at the top surface. The amount of time between heating events was identified as a key parameter that affects the temperature distribution at the bottom surface. Cooling between heating events helps to reduce maximum temperatures but can increase spatial variations in the temperature profile. Directional temperature gradients were calculated in each direction using the temperature fields and the finite difference method. Contrary to results in the literature, the z-direction gradient, ∂T∂z, dominated the other two components and is the primary driver of residual stress production inside a printed part. The magnitude of the temperature gradient, |∇T|, was used to identify areas of localized residual stress. The total temperature gradient was highest near the laser position due to the ∂T∂z term. Moving away from the laser position rapidly decreases |∇T|, which could develop residual stress inside the printed part. An improved understanding of temperature fields and residual stress inside the part during printing will yield more consistent part geometry, and fewer failed prints due to distortion from residual stress.

Abstract Gaseous flow in micro-scale systems comprised of moving components experience Fluid-Structure Interaction (FSI) and rarefaction when the length scales are small. While many commercial codes claim the ability to simulate FSI problems, such a combination is very challenging to model. Here we propose a momentum exchange coefficient model within the FSI algorithm, MPM-ICE, that enables the simulation of rarefied flow. The proposed model was derived using the Maxwell first-order velocity slip boundary condition. The model is verified using analytical solutions for pressure-driven Poiseuille and Couette planar flow. In addition, the model is validated using experimental pressure data of microchannel gas flow and DSMC simulation results. Unlike the previous model, the proposed model is more robust and is nearly insensitive to the grid size and the solid particle distribution around the surface. In addition, the model is universal since it is applicable for flow in the continuum and slip regimes.

Each year, more and more objects are put into Earth orbits. As the Earth orbits become more crowded, the potential for disastrous collisions between orbiting objects increases. The most problematic objects are space debris objects, which often cannot control themselves and can have a natural lifespan of many years. Several methods of actively eliminating space debris have been investigated, but early tests have not yielded promising results. The omnidirectional magnetic field generator, or Omnimagnet, is a novel electromagnetic device that can manipulate space debris without physical contact. Such a technique is safer and more reliable for satellites than alternative methods that require contact. However, the Omnimagnet is expected to be thermally limited because it generates large amounts of Joule heating. Using forced air convection cooling on Earth, the device is prone to rapidly overheating at high electrical loads. The vacuum environment of space creates radically different thermal conditions to those on Earth, and currently, there is no understanding of Omnimagnet thermal performance in space. It is unknown how much current can be supplied to an Omnimagnet in space before overheating occurs. To address this knowledge gap, this study presents a 1D, steady-state thermal resistance model to predict Omnimagnet thermal performance. Contact resistances, conduction resistances, and radiative resistances have been considered. This model is then used to determine the maximum safe driving current, 1.95A, which avoids overheating. Additionally, thermal resistances are compared to determine the limiting heat transfer mechanisms within the device. Radiative resistances dominate the problem, and thus thermal management strategies should focus on improving radiative heat transfer. Two such strategies, increased emissivity and additional radiating area, are investigated using the thermal model. These thermal management strategies increase the maximum safe current by 26% and 107%, respectively. The thermal resistance model demonstrates that Omnimagnets may be valuable tools to reduce the proliferation of space debris orbiting Earth.

The fluid dynamic and thermal performance of a circular cylinder with a slot parallel to the flow is nu-merically investigated. The study utilized the semi-implicit finite volume multi-material algorithm MPM-ICE, a component of the Uintah framework. The normalized slot width s/D ranges from 0.1 -0.3, introduc-ing an additional heat transfer surface area between -10 and -50%, and a mass reduction between -13 and -38% in the cylinder. We assumed two-dimensional incompressible flow and simulated a Reynolds number ReD between 100 and 10 0 0. The slotted cylinders are found to have a total drag force reduction up to -45%, compared to a solid cylinder despite the additional viscous drag force in the slot. Convection heat transfer is enhanced up to -70%. The slotted cylinder performance index, defined as the ratio of the heat rate to the drag force, increases up to maximum of -3, indicating better overall thermal fluid per-formance. An entropy analysis showed the best performance index occurs at the highest ReD. Correlations for drag coefficient and Nusselt number are proposed along with an entropy optimization method.(c) 2023 Elsevier Ltd. All rights reserved.

Spatially resolved temperature measurements and understanding the local heat-affected zone (HAZ) are of urgent importance in metal additive manufacturing (AM). Many experiments have used infrared (IR) temperature measurements at the build surface, but there is little experimental work measuring temperatures below the surface. Measurements below the top surface are vital to understand how the heating of additional build layers affects the temperature history of previously printed layers, especially in thin geometries. A thin metal plate with incident laser power can reasonably represent such thin geometries, for example, an overhang feature of an actual part undergoing laser powder bed fusion (LPBF). As a part of this work, we describe the design, construction, and calibration of an experimental setup that allows direct measurement of temperature distributions on the bottom side of a metal substrate. This is accomplished using a high-speed IR camera (2000 fps) positioned below a thin Inconel 625 substrate of known thickness (500 μm) and emissivity. The top side is irradiated with a high-power ytterbium fiber laser, while temperature distributions are measured on the bottom surface. The local temperature on the bottom side is resolved with a spatial resolution of 200 μm in the x and y directions. Local temperature distributions and HAZ dimensions are reported for single-track scans as a function of the laser power. The insights derived from this study will ultimately establish a fundamental link between laser processing parameters, local thermal history, and printed part properties.

Omni-directional magnetic field generators (or Omnimagnets) are devices with several potential applications, such as capsule endoscope and magnetic guidance of a cochlear implant. An Omnimagnet heats due to the Joule effect and the resulting excessive temperatures may cause device failure. Thermal analysis of an Omnimagnet can provide operational limits to prevent device failure due to excessive heating; however, as the device is still new, the thermal performance of the Omnimagnet has not yet been completely studied. The thermal behaviour of two Omnimagnets with some structural differences are numerically and experimentally studied in this work. A lumped-capacitance model is validated with experimental results showing the model Normal Root Mean Square Error for both Omnimagnets to be less than 12 $$\%$$ . Results show that increasing the size of the Omnimagnet by about 16 $$\%$$ , slows the rate of temperature increase within the Omnimagnet by 44 $$\%$$ . In addition, a constant frame temperature heat sink at 0  $$^\circ$$ C decreases the steady-state temperature of the outer solenoid by approximately 29 $$\%$$ when the outer solenoid is powered at 10 A.

Heat transfer and flow characteristics for a two-dimensional ellipse of different aspect ratios with single slot aligned with the principal flow direction is investigated numerically. In this study we quantify the change in drag force and heat transfer rate due to the slot. The ellipsoid aspect ratios are 1.0 (circle), 0.75, and 0.5 and the normalized slot height S/a, where S is the slot height and a is the minor-axis length of the ellipsoid, is 0.2. For each aspect ratio, simulations are conducted for both the slotted and solid ellipsoids. Two-dimensional incompressible airflow for Reynolds numbers Rea (based on minor-axis length a) between 100 and 1000 is modeled assuming an isothermal ellipsoid. A maximum drag force reduction of ∼11%, ∼25%, and ∼40% is found for aspect ratios of 0.5, 0.75, and 1.0, respectively, at Rea = 1000. At the same Rea, a maximum heat rate increase of ∼74%, ∼73%, and ∼69% is found for aspect ratios of 0.5, 0.75, and 1.0, respectively. The change in the performance index, defined as the ratio of the heat rate to the drag force, increases up to maximum of ∼1.96, ∼2.33, and ∼2.83 for aspect ratios of 0.5, 0.75, and 1.0, respectively, at Rea = 1000. The improvements are the result of the increased heat transfer area and the reduction in the total drag force, due to the flow interaction with the wake near the exit of the slot. An entropy analysis shows that an ellipsoid, aspect ratio of 1.0, has the best overall thermodynamic performance for 400 ≤ Rea ≤ 1000, whereas the ellipsoid of aspect ratio of 0.5 has the least entropy generation for 100 ≤ Rea ≤ 400. Finally, the ellipsoid with an aspect ratio of 1.0 benefits the most through the addition of the slot, inferring that this feature is most suited to bluff bodies.

The hydrodynamic and thermal performance of a circular cylinder with slots of different configurations in transverse flow is investigated. The first configuration consists of a cylinder with two slots, one aligned with the flow and the other in a perpendicular arrangement (two orthogonal slots). Each slot has a normalized slot width s/D = 0.2, where D is the cylinder diameter. The second configuration consists of a cylinder with two parallel slots aligned to the transverse free stream flow. The two slots are sized at s/D = 0.1 and are symmetrically placed on both sides of the cylinder centerline. The slots introduce additional heat transfer surface area between ~77% and ~109% for the orthogonal-slots and parallel-slots, respectively. Two-dimensional incompressible airflow for Reynolds numbers between 100 and 1000 is numerically simulated. The slotted cylinders are found to have a total drag force reduction up to ~30%, compared to a solid cylinder despite the additional viscous drag force of the slots. Convection heat transfer rate is enhanced up to ~81% and ~100% for the orthogonal-slot and the parallel-slot cylinders, respectively. Combining the hydrodynamic and thermal changes associated with the slotted cylinders, the performance index, defined as the ratio of the normalized heat rate to the normalized drag force, increases up to maximum of ~2.4 and ~2.8 for the orthogonal-slot and the parallel-slot cylinders, respectively, indicating better overall thermal-fluid performance. This enhancement is due in part to the additional heat transfer surface area and the reduced pressure drag from increased downstream external pressure caused by the interaction of the slot exhaust with the flow in the wake region. The easily fabricated, slotted cylindrical fins are capable of enhanced overall performance for cooling applications, such as electronic component heat dissipation.

In traditional cochlear implant surgery, physical trauma may occur during electrode array insertion. Magnetic guidance of the electrode array has been proposed to mitigate this medical complication. After insertion, the guiding magnet attached to the tip of the electrode array must be detached via a heating process and removed. This heating process may, however, cause thermal trauma within the cochlea. In this study, a validated three-dimensional finite element heat transfer model of the human cochlea is applied to perform an intracochlear thermal analysis necessary to ensure the safety of the magnet removal phase. Specifically, the maximum safe input power density to detach the magnet is determined as a function of the boundary conditions, heating duration, cochlea size, implant electrode array radius and insertion depth, magnet size, and cochlear fluid. A dimensional analysis and numerical simulations reveal that the maximum safe input power density increases with increasing cochlea size and the radius of the electrode array, whereas it decreases with increasing electrode array insertion depth and magnet size. The best cochlear fluids from the thermal perspective are perilymph and a soap solution. Even for the worst case scenario in which the cochlear walls are assumed to be adiabatic except at the round window, the maximum safe input power density is larger than that required to melt 1 mm3 of paraffin bonding the magnet to the implant electrode array. By combining the outcome of this work with other aspects of the design of the magnetic insertion process, namely the magnetic guidance procedure and medical requirements, it will be possible to implement a thermally safe patient-specific surgical procedure.

Magnetic guidance of cochlear implants is a promising technique to reduce the risk of physical trauma during surgery. In this approach, a magnet attached to the tip of the implant electrode array is guided within the scala tympani using a magnetic field. After surgery, the magnet must be detached from the implant electrode array via localized heating, which may cause thermal trauma, and removed from the scala tympani. Objectives: The objective of this work is to experimentally validate a threedimensional (3D) heat transfer model of the scala tympani which will enable accurate predictions of the maximum safe input power to avoid localized hyperthermia when detaching the magnet from the implant electrode array. Methods: Experiments are designed using a rigorous scale analysis and performed by measuring transient temperatures in a 3D-printed scala tympani phantom subjected to a sudden change in its isothermal environment and localized heating via a small heat source. Results: The measured and predicted temperatures are in good agreement with an error less than 6% ( p = 0.84). For the most conservative case where all boundaries of the model except the insertion opening are adiabatic, the power required to release the magnet attached to the implant electrode array by 1 mm3 of paraffin is approximately half of the predicted maximum safe input power. Conclusions: A 3D heat transfer model of the scala tympani is successfully validated and enables predicting the maximum safe input power required to detach the magnet from the implant electrode array. Significance: This work will enable the design of a thermally safe magnetic cochlear implant surgery procedure.

An Omnimagnet is an electromagnetic device that enables remote magnetic manipulation of devices such as medical implants and microrobots. It is composed of three orthogonal nested solenoids with a ferromagnetic core at the center. Electrical current within the solenoids leads to undesired temperature increase within the Omnimagnet. If the temperature exceeds the melting point of the wire insulation, device failure may occur. Thus, a study of heat transfer within an Omnimagnet is a necessity, particularly to maximize the performance of the device. A transient heat transfer model that incorporates all three heat transfer modes is proposed and experimentally validated with an average normalized root-mean-square error of less than 4% (data normalized by temperature in degree celsius). The transient model is not computationally expensive and is applicable to Omnimagnets with different structures. The code is applied to calculate the maximum safe operational time at a fixed input current or the maximum safe input current for a fixed time interval. The maximum safe operational time and maximum safe input current depend on size and structure of the Omnimagnet and the lowest critical temperature of all the Omnimagnet materials. A parametric study shows that increasing convective heat transfer during cooling, and during heating with low input currents, is an effective method to increase the maximum operational time of the Omnimagnet. The thermal model is also presented in a state-space equation format that can be used in a real-time Kalman filter current controller to avoid device failure due to excessive heating.

Magnetic cochlear implant surgery requires removal of a magnet via a heating process after implant insertion, which may cause thermal trauma within the ear. Intra-cochlear heat transfer analysis is required to ensure that the magnet removal phase is thermally safe. The objective of this work is to determine the safe range of input power density to detach the magnet without causing thermal trauma in the ear, and to analyze the effectiveness of natural convection with respect to conduction for removing the excess heat. A finite element model of an uncoiled cochlea, which is verified and validated, is applied to determine the range of maximum safe input power density to detach a 1-mm-long, 0.5-mm-diameter cylindrical magnet from the cochlear implant electrode array tip. It is shown that heat dissipation in the cochlea is primarily mediated by conduction through the electrode array. The electrode array simultaneously reduces natural convection due to the no-slip boundary condition on its surface and increases axial conduction in the cochlea. It is concluded that natural convection heat transfer in a cochlea during robotic cochlear implant surgery can be neglected. It is found that thermal trauma is avoided by applying a power density from 2.265 × 107 W/m3 for 114 s to 6.6×107 W/m3 for 9 s resulting in a maximum temperature increase of 6°C on the magnet boundary.

Heat exchangers with mini- and micro-channel components are capable of high energy exchange due to their incumbent large surface area to volume ratio. Concurrently, recent advances in additive manufacturing simplify the creation of metallic minichannels that incorporate turbulators for heat transfer enhancement. As part of the development of a minichannel heat exchanger with turbulators, this study analyzes the three-dimensional conjugate heat transfer and laminar flow in a minichannel heat exchanger equipped with rectangular winglet vortex generators (VGs) through numerical simulation. The minichannels have a hydraulic diameter of 2.86 mm and are assumed to be made from aluminum alloy AlSi10Mg. This material is one of the popular alloys in the additive manufacturing industry (three-dimensional (3D) printing) because of its light weight and beneficial mechanical and thermal properties. The working fluid is distilled water with temperature-dependent thermal properties. The minichannel is heated by a constant heat flux of 5 W cm(-2) and the Reynolds number is varied from 230 to 950. The simulations are performed using the COMSOL platform, which solves the governing mass, momentum, and energy equations based on the finite element method. The effect of the VG design parameters, which include VG angle of attack, height, length, thickness, longitudinal pitch, and distance from the sidewalls, is investigated. It is found that the generation of three-dimensional vortices caused by the presence of the vortex generators can notably boost the convective heat transfer, at the cost of increased pressure drop, potentially reducing the heat exchanger size for a given heat duty. A sensitivity analysis indicates that the angle of attack, VG height, VG length, and longitudinal pitch have the most significant effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and distance from the sidewalls only had minor influences on the heat exchanger performance over the studied range of design parameters.

An Omnimagnet is comprised of three orthogonal nested solenoids that enables magnetic guidance of devices such as medical implants. Electrical current within the solenoids leads to Joule heating resulting in undesired temperature increase within the Omnimagnet. If the temperature exceeds the melting point of the solenoid wire insulation, device failure will occur. Thus, a study of the heat transfer within an Omnimagnet is a necessity. In the present study, a thermal transient model was developed and validated with experimental data with maximum normalized root mean square error equal to 2.3%. A parametric study revealed that a reasonable operational range of input current for the tested Omnimagnet without active cooling is 0 to 9 A. At current higher than 9 A the maximum operational time is less than 2.5 min. Providing cooling to the Omnimagnet frame during heating or increasing convective cooling during cool down are effective methods to increase the maximum operational time of the Omnimagnet.

Polymerase Chain Reaction (PCR) is used to amplify a specific segment of DNA through a thermal cycling protocol. The PCR industry is shifting its focus away from macro-scale systems and towards micro-scale devices because: micro-scale sample sizes require less blood from patients, total reaction times are on the order of minutes opposed to hours, and there are cost advantages as many microfluidic devices are manufactured from inexpensive polymers. Some of the fastest PCR devices use continuous flow, but they have all been built of silicon or glass to allow sufficient heat transfer. This article presents a disposable polycarbonate (PC) device that is capable of achieving real-time, continuous flow PCR in a completely disposable polymer device in less than 13 minutes by thermally cycling the sample through an established temperature gradient in a serpentine channel. The desired temperature gradient was determined through simulations and validated by experiments which showed that PCR was achieved. Practical demonstration included amplification of foot-and-mouth disease virus (FMDV) derived cDNA.

Flow around a rigid, truncated, wall-mounted cylinder with an aspect ratio of 5 is examined computationally at various Reynolds numbers Re to determine how the end effects impact the vortex shedding frequency. The existence of the wall and free end cause a dampening of the classical shedding frequency found for a semi-infinite, two-dimensional cylinder, as horseshoe vortices along the wall and flow over the tip entrain into the shedding region. This effect was observed for Reynolds numbers in the range of 50 to 2000, and quantified by comparing the modified Strouhal numbers to the classical (two-dimensional) solution for Strouhal number as a function of Reynolds number. The range of transition was found to be 220 < Re < 300, versus 150 < Re < 300 for the classical ease. Vortex shedding started at Re approximate to 100, significantly above Re = 50, where shedding starts for the two-dimensional case.